Shaping drum for crown reinforcement plies

ABSTRACT

A drum ( 1 ) of variable diameter of generally cylindrical form, intended for the assembly of the belt plies and profiled elements constituting the crown of a tyre, comprising a set of first holding means ( 3 ) arranged circumferentially at the equator of the drum and suitable for making that part of the ply arranged level with these means adhere to the surface of the drum, and characterised in that it comprises a set of second holding means ( 4 ) suitable for making that part of the ply placed level with said second means alternately adhere to or slide freely on the drum, and which are arranged circumferentially and axially on either side of said equator over the entire surface of said drum ( 1 ).

The invention relates to the field of the manufacture of tyres, and inparticular the field of the manufacture of crown reinforcement belts.These crown reinforcement belts are usually composed of one or moreplies stacked one on another. Each of these plies is formed from cableswhich are parallel to each other and are coated in a rubber-nature mix.These cables form a given angle with the circumferential direction ofthe tyre. The cables may be constituted of one or more strands, whichthemselves are formed from unit cords made of textile or more generallyof metal in the case of crown reinforcement plies.

In order to impart the expected qualities to the tyre, the reinforcementbelts are generally formed of at least two plies the cables of whichform, relative to the circumferential direction, angles having oppositesigns, of absolute values which are close to one another but notnecessarily identical. Once in place, these plies effect triangulationwith the plies of the carcass reinforcement, the cables of whichgenerally form an angle of 90° with the longitudinal direction.

According to the manufacturing processes commonly used in the tyreindustry, the crown reinforcement plies are laid after the carcassobtained in a first stage has been shaped, that is to say after a toricform has been imparted to the tyre blank of substantially cylindricalform. Said carcass generally comprises a carcass reinforcement plyanchored at its two ends to rings for reinforcing the bead.

The belt plies are laid when the diameter of the blank is close to thedefinitive diameter of the tyre. This diameter is calculated to permitinsertion of said final blank in the vulcanisation press.

Another method consists of producing the whole of the crown on acylindrical form referred to as a crown form, the diameter of which isalso close to the definitive diameter, and on which are deposited insuccession the crown reinforcement plies and the profiled elementsconstituting the crown section of the tyre and comprising, inter alia,the tread. The finished crown is then transferred by a transfer ring tothe carcass which, by conforming thereto, adheres to the inner part ofthe crown.

On the other hand, and still with the aim of improving the performanceof the tyres, the advantage of producing crown plies the reinforcementcables of which have angles which are variable over their length hasbeen demonstrated. More particularly, the angle of the reinforcingthreads relative to the longitudinal direction is less at the centrethan on the edges of the ply. The effect of this S-shaped arrangement isto facilitate the flattening of the tyre by improving the comfort andthe stability, and to reduce the wear phenomena at the ply edge. Thistype of tyre is described by way of example in patent FR 2 037 520 oralternately in patent EP 312 300.

The mechanisms linked to the triangulation of the plies are widely knownto the person skilled in the art, and are the subject of numerouspublications, among which mention will be made of publication FR 2 797213 of the Applicant.

A process for producing this particular form of crown belt is set forthin the aforementioned patent FR 2 037 520. It consists of depositing twocrown reinforcement plies one on the other, making them adhere stronglyover their entire length and over part of their width, and stretchingthe whole in the longitudinal direction. One variant of this processconsists of including a separating element over part of the width, so asto permit sliding of the plies and to define the zones of the ply edgein which it is desired to modify this angle. Once stabilised, the ply islaid directly on the carcass of the tyre which has beforehand beencurved into its toric form.

It will be observed that this process necessitates assembling the plieson an independent station, but also that producing the join of the twoends of the assembly thus produced may prove awkward owing to thesuperposition of plies of different angles.

The process described in application FR 2 797 213 makes it possible toproduce a crown having the characteristics set forth above, but it isaccompanied by the deradialisation of the carcass reinforcement plybeneath the crown zone.

The invention which is the subject of the present application relates toa process and a device for producing an assembly on a crown form of thecrown reinforcement plies the cables of which form variable angles withthe circumferential direction over their length, while preciselycontrolling the geometry and the position on the drum for laying thering thus obtained.

To this end, it is proposed to effect separately the assembly of theelements constituting the crown of the tyre on a drum of variablediameter of generally cylindrical form, comprising a set of firstholding means arranged circumferentially on the equator of said drum andsuitable for making that part of the ply arranged level with these meansadhere to the drum and characterised in that it comprises a set ofsecond holding means which are suitable for making that part of the plyplaced level with said second means alternately adhere to or slidefreely on the drum, and which are arranged circumferentially and axiallyon either side of the equator over the entire surface of said drum.

The crown belt plies are assembled by positioning the drum at a firstdiameter. The first crown belt reinforcement ply, the reinforcementcables of which form a given angle with the circumferential direction,is deposited while activating the first and second means so as to makethe entire ply adhere to the surface of the drum.

Then the second crown belt ply, composed of reinforcement cables formingwith the circumferential direction a given angle of the opposite sign tothe angle of the reinforcing threads forming the first ply, isdeposited. Then the second ply is made to adhere strongly to the firstply.

While keeping the first means in the preceding configuration, the secondmeans are activated so as to permit sliding of the first ply level withsaid second means, and the drum is positioned at a second diametergreater than the first diameter.

It has been shown that, in order to retain a precise alignment of theaxis of the plies with the circumferential direction, it was necessaryto hold this central part securely during the shaping operation whilepromoting sliding of those parts located on either side of this axis soas to permit triangulation of the plies involving a variation in theirwidth and in the angle of the cables forming them.

Thus everything happens as if each cable were performing a rotarymovement about its central part, said central part being held securelyin position on the surface of the drum by said first means. Furthermore,the free sliding of the lateral parts promotes the triangulation of theplies in a homogeneous and reproducible manner over the entirecircumference of the drum.

It thus becomes easy to continue the finishing of the crown of the tyreby depositing the rest of the products constituting said crown on thesame drum. These products may comprise other crown reinforcement plieswhich may form a possibly zero angle with the circumferential directionbut also rubber profiled elements, including the tread of the tyre.

It is therefore not necessary to effect the triangulation of the crownreinforcement plies on a different means from the one used for buildingthe crown. Furthermore, the use of this device proves particularlyadvantageous in precisely controlling the geometric position of theproducts constituting the crown relative to each other, but alsorelative to a reference on the drum.

The final production of the tyre then takes place entirelyconventionally by gripping the crown thus produced using a transfer ringand depositing it on the shaped carcass.

A drum in accordance with the invention is described briefly hereafterwith reference to the figures, in which

FIG. 1 is a diagrammatic front view of a drum in accordance with theinvention positioned at its first diameter,

FIG. 2 is a diagrammatic front view of a drum in accordance with theinvention positioned at its second diameter,

FIG. 3 is a diagrammatic perspective view of the drum positioned at itsfirst diameter,

FIG. 4 is a diagrammatic perspective view of the drum positioned at itssecond diameter,

FIG. 5 is a front view of a drum at its first diameter on which crownreinforcement plies have been deposited,

FIG. 6 is a front view of a drum at its second diameter on which crownreinforcement plies have been deposited,

FIGS. 7 to 9 are diagrammatic views of the main phases of operation ofthe holding means.

The drum 1 shown in FIG. 1 comprises a set of elements 2 arrangedequidistantly about an axis of rotation XX′. These elements are radiallymobile and make it possible to vary the substantially cylindricalsurface of the drum from a first diameter D1 to a second diameter D2.

Each element 2 has in its axial direction receptacles 20, into which areplaced the first holding means 3 and the second holding means 4respectively.

The first holding means 3 are arranged axially in the middle of each ofthe elements 2, which makes it possible to form a set of first holdingmeans arranged circumferentially on the equator EE′ of the drum 1. Theequator is defined as the intersection of a plane, perpendicular to theaxis of rotation XX′ of the drum and extending axially in the middle ofthe surface of the drum, with the cylinder formed by the surface of saiddrum.

An example of embodiment of a first holding means 3 is shown in FIG. 7and can be likened to a tyre valve 40. The body of the valve 40, ofsubstantially radial axis AA′, is arranged in the receptacle 20 of theelement 2. The body of the valve 40 comprises a series of orifices 45located on its lateral part. The orifices communicate with a chamber 46.

The body of the valve contains a tubular slider 41 which slides alongthe same axis AA′ and comprises at each of its ends a seat 43 and anoutlet 47 respectively. The seat of the slider 43 lies on the bearingsurface 44 under the action of the spring 42, and prevents air frompassing between the orifices 45 and the chamber 46. The body of theslider 41 comprises a conduit which connects the chamber 46 and theoutlet 47. The outlet 47 is arranged so as to be radially slightly tothe outside of the plane formed by the surface of the element 2. Theorifices 45 are connected to a vacuum source (not shown).

Thus, as shown in FIG. 8, by depositing a ply N1 on the surface of theelement 2, the slider 41 is retracted by forcing it back radiallytowards the inside. The effect of this action is to detach the seat 43of the slider from its bearing surface 44, and to connect the chamber 46and the orifices 45, which produces a partial vacuum at the outlet 47 ofthe slider. The arrows in FIG. 8 show the circulation of the air. Theresult is an adhesion force due to partial vacuum which flattens the plyagainst the surface of the drum, depriving it of any opportunity ofaxial displacement in the immediate vicinity of the outlet 47.

The second means are similar to the first means. They are arrangedaxially on either side of the equator EE′. They nevertheless differ fromthe first means 3 in that the orifices 45 may be connected alternatelyto a vacuum source and function like suction cups, as explainedpreviously, or to a pressurised air source. In this second case, theoperation of the second means is illustrated in FIG. 9.

The slider 41 is held in the retracted position by the action of the plyN1 on the outlet 47. The air can then circulate freely in the directionof the arrows from the orifices 45 towards the outlet 47. As a result, athin cushion of air is created between the surface of the element 2 andthe ply N1, the effect of which is to promote the sliding of the ply onthe surface of the drum located in the immediate vicinity of the outlet47.

The setting of the spring 42 and of the air pressure at the entrance tothe orifices 45 is adjusted so as to permit closure of the communicationbetween the chamber 46 and the orifices 45 when the ply N1 is removed.

The realisation of first means and second means based on pneumaticsvalves proves particularly simple to carry out. However, consideringfirst means which are electromagnetic in nature, which may prove ofparticularly high performance when the belt plies of the crown are metalplies, is not ruled out.

FIG. 2 shows the drum 1 positioned at its diameter D2, and FIGS. 3 and 4show the drum 1 at the diameters D1 and D2 in a perspective view. Themechanisms controlling the radial movement of the elements 2, and alsothe means enabling the drum to be supported and caused to rotate aboutthe axis XX′ are widely known to the person skilled in the art and arenot the subject of the present description, and so are not shown in thefigures.

FIGS. 5 and 6 show, in diagrammatic view, the stages of the shaping of acrown reinforcement belt composed of two plies N1 and N2 of widths L1and L2 respectively, L2 generally being less than L1. The reinforcementcables forming the plies form angles α1 and α2, of opposite signs, withthe circumferential direction.

The drum 1 is positioned at a first diameter D1 and the orifices 45 ofthe second means are connected to a vacuum connection. By depositing thefirst reinforcement ply N1, the outlets 47 of the sliders 41 are forcedback radially, the effect of which, as has previously been seen, is tokeep the ply N1 securely in position on the surface of the drum 1. Thecentre of the ply is also made to coincide with the equator EE′ so as toensure the geometric alignment of the constituents of the tyre relativeto a known reference.

Then a second ply N2 is deposited. So that the triangulation of theplies takes place in accordance with the geometric laws set forth by wayof example in the document FR 2 797 213 already cited, it is advisableto make the two plies adhere strongly to one another. It will be notedthat holding the plies in position on the surface of the drum duringthis operation is a way of preserving the geometric alignment impartedat the time of laying the plies.

Once this operation is finished, it is then possible to activate thesecond means in the configuration enabling the ply to be slid onto thesurface of the drum by connecting the orifices 45 of the second means toa pressurised air source. The first means remain in the previousposition, so as to keep those parts of the crown reinforcement beltwhich are located level with the equator EE′ securely in contact withthe drum and to prevent any movement of the belt level with the firstmeans. Holding the belt properly along the central circumference EE′ ofthe drum makes it possible to maintain the geometric alignment of theplies relative to a fixed reference on the drum 1.

By bringing the diameter of the drum to the diameter D2, thetriangulation of the plies, the width of which changes from L1 to L1′and from L2 to L2′ respectively, is brought about. The angles α1 and α2formed by the cables with the circumferential direction at the equatorchange respectively to the values α1′ and α2′ which are less than α1 andα2 respectively. These values α1′ and α2′ are substantially constantover the length of the cables, but it is observed that these anglesincrease greatly at each of the ends of the cables in the edge zone ofthe plies N1 and N2 to impart an S-shaped form to the cables of theplies. In practice, the difference between the angle formed by a cablewith the circumferential direction at its ends may vary from 2° to 15°compared with the angle formed by the same cable with thecircumferential direction at the centre of the ply.

Once the shaping of the belt has been carried out, the assembly of therest of the components forming the crown of the tyre takes place inconventional manner.

It is also observed that the pitch of the cables narrows. In otherwords, the distance between two consecutive cables substantiallyparallel to each other decreases during the phase of shaping the plies.And this phenomenon is more marked at the centre than on the ply edges.

The device as has just been described makes it possible to takeadvantage of this known phenomenon. This is because in reducing thepitch and increasing the cable density at the centre, the flexuralstrength of the crown is increased and the wear life of the tyreimproved.

This also makes it possible to adjust the pitch of the plies to justwhat is necessary. This is because, starting from a ply N1 having agiven pitch P1, it is possible to produce belts having an infinitenumber of pitches by modifying the shaping ratio. The shaping ratio isequal to the ratio of the second diameter D2 and the first diameter D1.In practice, the shaping ratio may vary between 1.03 and 1.5.

Thus, given knowledge of the pitch P1 of the ply N1, the angle α1′, thewidth L1′, the final pitch P1′ of the ply N1 (or the cable density whichit is desired to obtain at the centre of the tyre) and the finaldiameter D2, it is easy consequently to adjust the width L1, the angleα1, and the laying diameter D1. In practice, it is possible to obtain apitch P1′ of between P1 and 0.75*P1.

This method of implemention makes it possible, at the same time, tosimplify the industrial complexity by reducing the reference number ofplies of different pitches P1, and to give additional room for manoeuvrein the choice of cables which it becomes possible to select from amongcables of lesser diameter, the use of which is permitted by increasingthe density by shaping, in accordance with the process which is thesubject of the invention, so as to obtain a structural resistancesimilar to that which would have been obtained with cables of greaterstrength and of a greater pitch.

1. A drum (1) of variable diameter of generally cylindrical form,intended for assembly of the belt plies (N1, N2) and profiled elementsconstituting the crown of a tyre, comprising a set of first holdingmeans (3) arranged circumferentially at the equator of the drum EE′ andsuitable for making that part of the ply (N1) arranged level with thesemeans adhere to the drum, and characterised in that it comprises a setof second holding means (4) suitable for making that part of the plyplaced level with said second means alternately adhere to or slidefreely on the drum, and which are arranged circumferentially and axiallyon either side of the equator EE′ over the entire surface of said drum(1).
 2. A drum according to claim 1, in which the first means (3) areformed by pneumatic valves opening on to the outer surface of said drum(1) and connected to a vacuum connection.
 3. A drum according to claim1, in which the first means (3) are formed by electromagnets.
 4. A drumaccording to claim 1, in which the second means (4) are formed bypneumatic valves opening on to the outer surface of said drum which areable to be connected alternately to a vacuum connection or to a pipesupplying pressurised air.
 5. A drum according to claim 1, formed byassembling a given number of radially mobile elements (2), on which saidfirst means (3) are placed axially in the middle of said element andsaid second means (4) are placed axially on either side of said firstmeans (3).
 6. A process for assembling a tyre, comprising a separatestep of producing the crown of said tyre on a drum of variable diameter(1) of generally cylindrical form, said drum comprising a set of firstholding means (3) arranged circumferentially at the equator EE′ of saiddrum and suitable for making that part of the ply arranged level withthese means adhere to the drum (1) and comprising a set of secondholding means (4) suitable for making that part of the ply placed levelwith said second means (4) alternately adhere to or slide freely on thedrum, and which are arranged circumferentially and axially on eitherside of the equator EE′ over the entire surface of said drum (1),characterised in that it comprises the following steps: positioning thedrum (1) at a first diameter D1, depositing a first crown belt ply N1composed of reinforcement cables coated in a rubber mix forming a givenangle α1 with the circumferential direction, by activating the first andsecond means so as to make the entire ply adhere to the surface of thedrum, depositing a second crown belt ply N2 composed of reinforcementcables coated in a rubber mix forming a given angle α2 of opposite signto the angle α1 with the circumferential direction, making the secondply N2 adhere to the first ply N1, while keeping the first means (3) inthe preceding configuration, activating the second means (4) so as topermit sliding of the first ply level with said second means (4),positioning the drum at a second diameter D2 greater than the firstdiameter D1, activating the second means (4) so as to make the plyadhere to the surface of the drum, depositing the other plies and theother profiled products constituting the crown of the tyre, gripping thecrown thus produced with a transfer ring and depositing the crown on atyre blank of toroidal form.
 7. An assembly process according to claim6, in which the shaping ratio, which is equal to the ratio between thesecond diameter D2 and the first diameter D1, is of between 1.03 and1.5.
 8. An assembly process according to claim 7, in which the angleformed with the circumferential direction by a cable at its two ends isgreater than the angle formed with the circumferential direction by thesame cable in its central part.
 9. An assembly process according toclaim 8, in which the angle formed with the circumferential direction bya cable at its two ends is greater by 2° to 15° than the angle formedwith the circumferential direction by the same cable in its centralpart.